1. INTRODUCTION:
Number of Schiff bases containing azomethine group and their complexes have been identified for their chelating abilities and biological properties.[1-3] Several Schiff base ligands with oxygen and nitrogen atoms in their backbone showed anticancer,[4-7] antibacterial,[8-12] antifungal,[13-15] and diuretic activities.[16] Many complexes of pyrazol-5-one derivatives such as antipyrine,[17-20] 4-dimethylaminoantipyrine, [21] 4-aminoantipyrine,[22-24] and 3-methyl-1-phenylpyrazol-5-one[25] have been synthesized and some of them found to be DNA cleavage agents. Moreover, the ligand or the metal in these complexes can be changed in an easily controlled manner to facilitate the individual applications.[26]
The synthetic protocol for the preparation of complexes derived from 4-aminoantipyrine, 3-hydroxy,4-ntrobenzaldehyde and acetylacetone involves three steps namely synthesis of β-diketone, Schiff base and metal complexes under reflux conditions. In the present work, effort has been made to synthesized new series of N2O2 type complexes derived from 4-aminopyridine, 4-nitrobenzaldehyde and acetylacetone using solid-supported perchloric acid as a catalyst in two steps.
2. EXPERIMENTAL:
2.1 MATERIAL AND METHODS OF ANALYSIS:
Analytical grade chemicals, 4-aminoantipyrine,
4-nitrobenzaldehyde, 4-chlorobenzaldehyde, 4-methoxybenzaldehyde, acetylacetone
and various metal salts were purchased from Sigma-Aldrich, INC. IR spectra
(400–4000 cm-1) were recorded on Shimndzu FTIR spectrophotometer
using KBR discs, and the absorption bands are expressed in cm-1. 1H
NMR spectra were recorded in DMSO-d6 with tetramethyl silane as an
internal standard. CHN analysis of the compounds was recorded at the
Sophisticated Analytical Instrument Facility, (SAIF), Chennai. The X-band ESR
spectra of the complexes were recorded at 300 K on a Varian ESR
spectrophotometer using diphenylpicrylhydrazyl (DPPH) as internal standard at
RSIC, IIT, Chennai. Magnetic susceptibility measurements of the complexes were
carried out by Gouy balance using copper sulphate as the calibrant. The molar
conductance of the complexes was measured using a Systronic conductivity bridge
at room temperature in DMSO solution. TG/DTA scans were recorded on
Mettler-Toledo-851 TGA-DTA instrument at linear heating rate of 100
per minute under inert atmosphere in a temperature range 25-10000C.
X-ray powder diffraction patterns of complexes were recorded in the 2
range
of 10-800 on Bruker X-D 8 advanced diffractometer and XRD scans with
the help of powder X- programme. The antimicrobial activities of the ligand and
complexes were carried out by disc diffusion method.
2.2 Present Work:
A new series of complexes of N2O2 type have been synthesized via non-template condensation of 3(4’-nitrobenzalidene)-2,4-di(imino-4”-antipyrinyl)pentane and metal salt in presence of 10 mol% solid-supported perchloric acid (Scheme 3 and 4). The synthesized complexes were characterized and screened for their antimicrobial activity.
3. TYPICAL PROCEDURE:
3.1 Synthesis of 3(4’-chlorobenzalidene)-2,4-di(imino-4”-antipyrinyl)pentane (L2):
A mixture of acetyl acetone (10 mmol), 4-aminoantipyrine (20 mmol), and 4-nitrobenzaldehyde (10 mmol) along with 10 mol% solid-supported perchloric acid in ethanol (50 mL) was refluxed until completion of the reaction, as monitored by thin layer chromatography (TLC). The catalyst was filtered, washed with ethanol and the filtrate was concentrated under reduced pressure. The crude product was purified by recrystallization with hot ethanol.
3.2 Synthesis of Metal Complexes:
A mixture of 3(4’-nitrobenzalidene)-2,4-di(imino-4”-antipyrinyl)pentane (2 mmol), metal salt (2 mmol) along with 10 mol% solid-supported perchloric acid in ethanol (15 mL) was refluxed for 1 h. The resulting colored complex along with insoluble catalyst was filtered, wash with ethanol, acetone and petroleum ether. To separate the catalyst, complex was dissolved in DMSO (2 x 15 mL) and then filtered. The filtrate was then concentrated under reduced pressure to afford shiny blue colored copper complex, which was dried over calcium chloride (60%yield).